Method of heat treating nickel bearing aluminum bronze alloys



United States Patent METHOD OF HEAT TREATING NICKEL BEARING ALUMHNUMBRGNZE ALLOYS John F. Klement, Milwaukee, Wis, assignor to Arnpco Metal,Inc., Milwaukee, Wis., a corporation at Wrscousin No Dir-swing.Application May 9, 1056, tierial No. 583,627

4 Claims. (Cl. 148-==-1) This invention relates to a method of heattreating a nickel bearing aluminum bronze alloy.

The metallographic structure of an aluminum bronze alloy is controlledgenerally by the aluminum content. An alloy having an aluminum contentbelow 7 and without appreciable amounts of other alloying elements hasan alpha phase structure, while an aluminum content of 7.5% to 10.5%will produce the alpha and/or beta phase depending on the heat treatmentto which the alloy is subjected. An aluminum content in excess of about10.5% will generally result in only a beta phase structure. The additionof aluminum absorbing elements, such as nickel, manganese or the like,would require an aluminum range of about 8.5% to 11.5% in order toobtain the duplex alpha and beta phase.

The alpha phase provides the aluminum bronze alloy with excellent coldworking strength and imparts ductility to the alloy, while the betaphase provides excellent hot working properties and imparts hardness tothe alloy.

If a nickel-bearing aluminum bronze alloy, having an aluminum content of8.5% to 11.5% is quenched from the solidus temperature of about 1870 F.all beta phase results. solidus temperature, a structure of about 90%alpha and 10% beta is produced.

An object of the present invention is to control the cooling rate of thealuminum bronze alloy in order to obtain a metallographic structurehaving about 50% to 60% alpha and the remainder of beta in the cooledalloy. It has been found that this proportion of 50% to 60% alphaprovides an alloy having the most desirable combination of strength andductility. An alpha to beta ratio such as this is particularly useful ina weld deposit employed to weld thick sections of aluminum bronze plate,for this ratio tends to eliminate crater cracking and base metalrupture.

The general composition of the aluminum bronze alloy to be subjected tothe treatment of the present invention is as follows, in weight percent:

Percent Aluminum 8.5l0.5 Iron 3.0-6.0 Nickel 3.0-6.0 Manganese 0.5-1.5Copper Balance A specific example of the composition of the alloyfalling within the above range is as follows:

Percent Aluminum a- 9.5 lron 4.0 Nickel 4.0 Manganese 1.0 Copper BalanceThe aluminum content set forth above provides an alloy having hightensile strength and yield strength coupled with good elongation. iscontrolled by the aluminum content as well as the iron,

However, if the alloy is slowly cooled from the The relationship ofalpha to beta ICQ nickel and manganese. The iron and nickel increase thestrength of the alloy, and the iron also produces a fine, tough grainstructure, while the manganese aids in improving the fluidity andsoundness of the alloy.

The procedure employed to bring about the desired alpha beta ratio is tocool the alloy from the solidus temperature of about 1870 F. down toabout 1300 F. at a cooling rate of 400 F. to 550 F. per minute, orpreferably about 500 F. per minute. When the temperature of the alloyreaches about 1300 F. the rate of cooling is reduced and the alloy iscooled down to a temperature of about 800 F. at a rate of F. to 150 F.per minute and preferably about F. per minute. The alloy is then cooledfrom 800 F. to room temperature at a rate of 25 F. to 75 F. per minuteand preferably about 50 F. per minute. This controlled rate of coolingresults in an aluminum bronze alloy having between 50% and 60% alpha inthe metallographic structure.

If the alloy is cooled at a rate greater than about 550 F. per minutefrom the solidus temperature down to about 1300 F. retained beta isproduced in the alloy which is extremely hard. The retained betadestroys the ability to form primary alpha so that the alpha coming outwhen the alloy is cooled from 1300 F. down to 800 F. will be acicularand the alloy will tend to be brittle.

If the cooling is too slow, less than about 450 F. per minute from thesolidus temperature to about 1300 F., an excessive amount of graingrowth results in the alloy which is undesirable. Therefore, it has beenfound that the cooling rate from the solidus temperature down to about1300 F. should be maintained within the 400 F. to 550 F. per minuterange in order to provide the proper start of nucleation.

If the alloy is cooled more rapidly than about 150 F. per minute fromabout 1300 F. down to about 800 F., the proper alpha size anddistribution is not: brought out. This results in the alpha particlesbeing too small and the alloy tends to become brittle. If the alloy iscooled at a slower rate than about 75 F. per minute from about 1300 F.to about 800 F. the kappa phase results and an A cooling rate in excessof about 75 F. per minute when cooling from about 800 F. down to roomtemperature produces stresses in the alloy which cause Warpage, ruptureor sensitivity to stress corrosion cracking. On the other hand, if thealloy is cooled too slowly, less than about 25 F. per minute, from about800 F. down to room temperature the beta transforms into eutectoid whichagain results in a brittle alloy.

On cooling from the solidus temperature of about 1870 F. the beta phaseappears and this has excellent hot working characteristics. In theneighborhood of 1600 to 1700 F. there will be approximately 90% beta andat this temperature the alloy will contract and expand with ease rttlueto the excellent hot working characteristics of the eta.

As the cooling progresses the 10%. alpha phase is enlarged toapproximately 30% at about 1300 F. and increases further to about 50%alpha at about 800 F. The beta phase controls the alloy as far as hotworking is concerned and below about 800 F. the strength and ductilityof the alpha phase will control the alloy down to room temperature.

The metallurgical characteristics of the alpha and beta constituentsmake the ratio workable. At elevated temperatures the beta has excellenthot working properties and a low Brinell hardness of approximately 80Brinell. As the alloy is cooled belowabout 800 F. the beta will increasein hardness until the temperature of the alloy has reached approximatelyF. At this latter temperature the alpha has a hardness of approxi mately80' Brinell. When the alloy is cooled to room temperature, the alphadeveloped by the controlled cooling has the ductilityneccssary todeform, while the beta has reached a maximum hardness of approximately250 Brinell and provides the alloy with strength.

' An example of the invention in the welding of a thick plate of analuminumbronze, alloy is as follows:

The base plate hada composition by weight of:

The heli-arc welding process was used to make the weld with a current ofabout 175 amperes. The temperature of the weld deposit was checked bytemple sticks and the rate of cooling maintained within theaforementioned ranges by use of a torch anneal to obtain a finalmetallographic structure of about 50% alpha and 50% beta.

The cooled weld deposit had a composition by weight of:

Percent Aluminum 8.5 Iron 4.5 Nickel 4.5 Manganese 1.0 Copper BalanceThe weld deposit had a tensile strength of 125,000 p. s. i., a yieldstrength of 60,000 p. s. i., an elongation in 2 inches of and a Brinellhardness of 200.

A slight variation in the weld rod composition may be necessary whenWelding heavier or lighter sections of base metal. The heavier sectionswhich afford a more rapid cooling should have an aluminum content ofapproximately 9.25%, while very thin sections will cool more slowly andcan have an aluminum content of about The ratio between beta and alphathat has been found to be most satisfactory for the weld deposit duringwelding of either light or heavy sections, is a 9 to 1 ratio be tweenbeta and alpha at 1650 F. At 1350 F. a ratio r of beta to alpha of 7 to3 is most desirable and at 850 F. the ratio which produces the best welddeposit is approximately a 1 to 1 ratio between beta and alpha. At roomtemperature, the most satisfactory ratio of beta to alpha is about 4 to6. In other Words, approximately 60% alpha and beta at room temperatureproduces the toughest and soundest weld deposits.

The method of weld deposit is not important, consequently carbon arc,metallic arc, consumable electrode and inert gas are have all beenemployed and satisfactory deposits will result if the proper ratio ofalpha to beta is maintained during cooling. The ratio is controlled bythe weld wire deposit and the technique of cooling and torch annealingto maintain the proper rate of cooling is essential. Throughexperimentation on the thickness of the section welded, the speed oftravel of the weld wire, and the current density, a welding techniquecan be developed using torch annealing to maintain the aforementionedcooling rates to bring about the desired alpha-beta relationship.

The thermal treatment of the invention can be applied to forgings,castings, rolled articles, etc. fabricated from the aforementionedcomposition as well as weld deposits. With a forging, for example, thetreatment can easily result in a tensile strength of 110,000 p. s. i., ayield strength of 55,000 p. s. i., an elongation in 2 inches of 20% anda Brinell hardness of 190.

Various modes of carrying out the invention are contemplated as beingWithin the scope of the following claims particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

I claim:

1. A method of heat treating a duplex phase aluminum bronze alloy of theclass described to produce a controlled ratio of alpha phase to betaphase in the metallographic structure, comprising; heating the alloy toa temperature above the solidus temperature thereof; cooling the alloyfrom the solidus temperature to a temperature of about 1300 F. at a rateof 400 F. to 550 F. per minute; cooling of the alloy from about 1300 F.to about 800 F. at a rate of from 75 to 150 F. per minute; and coolingthe alloy from about 800 F. to room temperature at a rate of 25 to 75 F.per minute.

2. A method of heat treating a duplex phase aluminum bronze alloy toproduce a controlled ratio of alpha phase to beta phase in themetallographic structure, said alloy having the following composition byweight:

Percent Aluminum 8.5 to 10.5 Iron 3.0 to 6.0 Nickel 3.0 to 6.0 Manganese0.5 to 1.5 Copper balance said method comprising; heating the alloy to atemperature above the solidus temperature thereof; cooling the alloyfrom the solidus temperature to a temperature of about 1300 F. at a rateof 400 F. to 550 F. per minute; cooling of the alloy from about 1300" F.to about 800 F. at a rate of from 75 to 150 F. per minute; and coolingthe alloy from about 800 F. to room temperature at a rate of 25 to 75per minute.

3. A method of heat treating a duplex aluminum bronze alloy to produce acontrolled ratio of alpha phase to beta phase in the metallographicstructure, said alloy having the following composition by weight:

Percent Aluminum 8.5 to 10.5 Iron 3.0 to 6.0 Nickel 1 c 3.0 to 6.0Manganese 0.5 to 1.5 Copper balance heating the alloy to a temperatureabove 1800 F, cooling the alloy from about 1800 F. to about 1300 F. at arate of about 500 F. per minute, cooling the alloy from about 1300" F.to about 800 F. at a rate of about F. per minute, and further coolingthe alloy from about 800 F. to room temperature at a rate of about 50 F.per minute to obtain about 50% to 60% alpha phase and the remainder betaphase in the metallographic structure.

4. A method of heat treating a duplex aluminum bronze alloy to produce acontrolled ratio of alpha phase to beta phase in the metallographicstructure, said alloy having the following composition by weight:

. Percent Aluminum 8.5 to 10.5 Iron 3.0 to 6.0 Nickel 3.0 to 6.0Manganese 0.5 to 1.5 Copper balance heating the alloy to a temperatureabove 1800 F. to provide a metallographic structure having about 10%alpha and the remainder beta, cooling the alloy rapidly to provide about30% alpha and the remainder beta at References Cited in the file of thispatent about 1300 F., further cooling the alloy at a reduced v d b th CD 1 e t rate to provide about 50% alpha and the remainder beta Alummumronze Issue y e Opper eve 0pm n d ,N 31 1939 31-57. at 800 F., andthereafter cooling the alloy slowly to room Assoc (Lon on) o pagestemperature to provide about 60% alpha and the re- 5 mainder betatherein.

2.A METHOD OF HEAT TREATING A DUPLEX PHASE ALUMINUM BRONZE ALLOY TOPRODUCE A CONTROLLED RATIO OF ALPHA PHASE TO BETA PHASE IN THEMETALLOGRAPHIC STRUCTURE, SAID ALLOY HAVING THE FOLLOWING COMPOSITION BYWEIGHT: